Impacts of specification of land cover and soil texture over the central Tibetan Plateau on land model simulations

Previous studies suggested the important role of land surface processes in modulating regional climate in Tibetan Plateau (TP), and therefore identifying and quantifying uncertainties in the land surface models are essential to improving climate models. Land cover and soil texture types are significant sources of modeling uncertainty due to the lack of detailed land surveys in TP. Moreover, it is generally ignored that the uncertainties in the specification of those surface types are intertwined with the uncertainties in the vegetation and soil parameters. To separate the effects of land cover or soil texture specification on the Noah with Multiple Parameterizations (Noah-MP) land model from uncertainties in model parameters, this study first identifies the most sensitive vegetation and soil parameters with a global sensitivity analysis method, and then conducts parametric ensemble simulations using two land cover datasets and two soil type datasets over the central TP to estimate the impact of changes in land cover or soil types on model responses. The distinction test and the Kolmogorov-Smirnov test are then applied to assess the differences between the results from two ensembles using different land cover or soil type datasets. Results show that the simulated energy and water fluxes over central TP are dominated by soil parameters. Canopy height is the most sensitive vegetation parameter, and the exponent in the function that relates soil water potential and water content is the most sensitive soil parameter. The differences between land cover datasets lead generally small differences in model outputs, except for replacing "snow and ice" by other types. Changes in soil types between loam and loamy sand produces the most significant change in simulations, and replacing silty clay loam by loam are the least significant. The work provides scientific reference for assessing the impacts of land cover or soil texture changes in Noah-MP simulations under future climate change.